1. Field of the Invention
This invention relates generally to techniques for maintaining downhole tools and their components within a desired temperature range in high-temp environments, and, more specifically, to an electrical submersible pumping system having a Stirling-Cycle cooling system.
2. Background Art
Electrical submersible pumping systems (ESPs) are used for artificial lifting of fluid from a well or reservoir. An ESP typically comprises an electrical submersible motor, a seal section (sometimes referred to in the art as a protector), and a pump having one or more pump stages inside a housing. The seal section (or protector) functions to equalize the pressure between the inside of the system and the outside and also acts as a reservoir for compensating the internal oil expansion from the motor. The protector may be formed of metal, as in a bellows device, or an elastomer. An elastomer protector is sometimes referred to as a protector bag.
In addition to motors, pump sections, and seals, a typical submersible pumping system may further comprise a variety of additional components, such as a connector used to connect the submersible pumping system to a deployment system. Conventional deployment systems include production tubing, cable and coiled tubing. Additionally, power is supplied to the submersible electric motor via a power cable that runs through or along the deployment system.
ESPs often incorporate the use of a gauge having one or more sensors and associated electronics for measuring and monitoring parameters related to the operation of the ESP and the production of fluid from the well or reservoir. These parameters may include, but are not limited to, motor temperature, well temperature, pump intake pressure, pump discharge pressure, and vibration. The gauge is typically located below the motor, from which it may draw electrical power. The sensors and associated electronics included in the gauge are housed in protective chamber to isolate them from well fluids and well conditions, such as high temperature (up to 350° F.) or pressure (up to 30,000 psi) which may compromise their operation. The power cable used to provide power to the motor may also be used as a means for transmitting data from the gauge to the surface, where the data are interpreted and the operational parameters of the ESP can be adjusted to optimize the production of fluid from the well or reservoir.
Currently, ESPs are rated for use up to 550° F., but the electronics controlling or monitoring the pump fails at these high temperatures and is generally not reliable above 300° F. These electronic components generally cannot function at high temperature without significant degradation of their lifetime or performance. These components are typically contained in a closed protective (insulating) chamber. The accumulation or transfer of heat into the chamber can raise the temperature inside the chamber to a point that exceeds the maximum operating temperature of the components. The heat source which raises the temperature inside the chamber may be the components themselves (e.g., electrical losses) or high temperature well fluids external to the tool.
In addition, in certain high temperature thermal recovery production methods, such as Steam Assisted Gravity Drainage (SAGD), ESPs will be subject to well temperatures exceeding the maximum operating temperature of the gauge (about 300° F.). These high temperatures may also destroy or weaken the seals, insulating materials, and other components of the submersible pumping system. Under these conditions, the use of a gauge for monitoring and optimizing production is compromised. This can have a substantial negative impact on the overall performance of a well and thus the economics of producing fluids from the well. As such, it is desirable to provide a means for cooling the gauge (or other components of a submersible pumping system) such that the operational temperature of the gauge and components is maintained within an acceptable temperature range conducive to reliable operation of the gauge in harsh operating environments.